What’s in this deep ‘blue hole’ off Florida? They’re working on

By Heather Murphy

Sprinkled across the ocean floor, invisible from the surface, are hundreds — or maybe thousands — of sinkholes. These “blue holes,” as scientists call them, do not swallow up everything incapable of fighting their gravitational force, like their black hole cousins. But to those who study them, they are still nearly as intriguing.

Recently, one particular blue hole — the Green Banana — has captured the imagination of many a land dweller. Headline after headline has offered a variation on the same theme: Scientists are flocking to a mysterious blue hole. One publication asked:“What Could It Be?”

What it is is the Green Banana, one of the deepest blue holes ever discovered, according to Jim Culter, a senior scientist at Mote Marine Laboratory, and it is on the verge of being studied in the most comprehensive way yet.

Soon scientists will venture into the Green Banana’s depths, where they hope to answer long-standing questions about whether the sinkhole — which extends around 275 feet, like an inverted, hourglass-shaped 20-story building, anchored in the ocean floor — connects to other sinkholes and whether freshwater flows within.

The scientists leading the mission to the sinkhole, which begins 155 feet below the ocean’s surface around 50 miles offshore from St. Petersburg, agree that the name, the Green Banana, sounds like it should be a bar in Key West. According to Larry Borden, a longtime commercial fisherman and boat captain who has known about the Green Banana for decades, the name emerged in the mid-1970s after a boat captain saw a green banana skin floating by a known “spring,” as fishermen referred to the underwater sinkholes back then.

One reason that so little is known about them, according to the National Oceanic and Atmospheric Administration, is that their entry points are often narrow — before they broaden out — making it impossible for an automated submersible to enter.

In the mission, which NOAA is funding, the plan is to carefully lower a 600-pound lander inside. Together the lander, which is shaped like a triangular prism, and divers will collect water and sediment samples and complete a biological survey, said Emily Hall, a scientist at Mote Marine Laboratory leading the mission.

“The excitement comes from the idea that this is exploration — we don’t know what we will see down there biologically and chemically,” she said. “We have an idea. But every time we go down there we find something new.”

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